Abstract:

The Kaapvaal Craton was the scene of two major magmatic events around 2.0 Ga,
namely the Bushveld Complex and the Phalaborwa Complex. Both complexes
have been the subject of numerous palaeomagnetic studies during and prior to the
1980s. Despite these studies, systematic inconstancies for emplacement ages, in
particular for the Bushveld Complex, have been found between the
palaeomagnetic findings and well constrained ages. The greatest concern with the
Bushveld Complex results are the large spread in pole positions previously
determined for the different zones. This has been interpreted in prior studies to
indicate that the Bushveld Complex was emplaced and cooled below the Curie
temperature of magnetite over a time span of 50 my. The results obtained
previously for the Phalaborwa Complex appear to be out of position (~16°) with
respect to those for the Bushveld Complex. This is of concern because new
geochronological data show that the Rustenburg Layered Suite of the Bushveld
Complex was emplaced approximately 1 my after the Phalaborwa Complex.
These inconsistencies have prompted the current re-investigation of the
palaeomagnetic results for both the Bushveld Complex and the Phalaborwa
Complex.
New palaeomagnetic data collected from all zones of the Rustenburg Layered
Suite from the Eastern, Northern and Western Lobes of the Bushveld Complex,
yielded palaeomagnetic poles that eliminated the spread in the apparent polar
wander path. This observation is in agreement with precise age data, constraining
the time period of emplacement of the complex to ~ 6 my. Resulting beddingcorrected
high blocking components from all zones produced better groupings,
thereby supporting a primary magnetic signature and indicating that the complex
was intruded in a near-horizontal position. Dual polarities identified within each
zone of the complex and positive reversal tests have identified one of the oldest
known reversals of the Earth’s magnetic field.
iii
Palaeomagnetic data from the Phalaborwa Complex have produced a pole position
that is in close proximity to those obtained from the coeval Bushveld Complex.
In an attempt to achieve a better understanding of tectonic events occurring in the
Kaapvaal Craton a number of dual polarity dykes within the Bushvled and
Phalaborwa Complexes were palaeomagnetic analysed. Results revealed that the
acquired pole positions are in agreement with ~1.9 Ga dykes, indicating the
possibility that the dykes occurring in both complexes are part of the same
magmatic event.
Palaeopoles generated during this study were used in refining the Kaapvaal Craton
apparent polar wander path around 2.0 Ga, and in conjunction with other welldefined
2.0 Ga poles for the Kaapvaal Craton, a robust cratonic pole was produced
that was used in Precambrian palaeographic reconstructions with emphasis on the
postulated Vaalbara continent and the Columbia supercontinent. Palaeomagnetic
reconstruction derived in this study has cast doubt on the existence of the
Vaalbara continent at 2.0 Ga. Although, some support is given to the existence of
the Columbia supercontinent at the same period.